1. Field of the Invention
The present invention relates to a rotary connector for electrically connecting a pair of housing, which are coupled to each other in such a manner as to be relatively rotatable, through a flexible cable, and more particularly, to a rotary connector for use in connection of a plurality of circuits mounted on a steering wheel of a vehicle including an air bag circuit and other circuits, such as a horn circuit or an automatic cruise control circuit.
2. Description of the Related Art
Rotary connectors of the above-described type generally include a pair of housings coupled to each other in such a manner as to be relatively rotatable, and include a belt-like flexible cable accommodated in an annular space defined between the two housings. The two ends of the flexible cable are electrically connectable to an exterior of from the housings when the flexible cable is fixed to the two housings. The flexible cable has a plurality of parallel conductors. A connector is connected to the end of the portion of the flexible cable which extends externally from the housing. Such a connector is generally a special connector connected to the end of the portion of the flexible cable which extends externally from the housing over a predetermined length. An alternate connector connected to the end of the externally extended portion of the flexible cable is the direct coupling type connector disclosed in U.S. Pat. No. 5,230,713. This connector has a plurality of terminals provided on the housing and is connected to the conductors of the flexible cable.
The rotary connector arranged in the manner described above is assembled in a steering device of a vehicle and is used as electrical connection means between various circuits, such as an air bag circuit or a horn circuit. In that case, one of the housings of the rotary connector is connected to a steering column (a stator), while the other housing is connected to a steering wheel (a rotor). The special connectors or direct connectors connected to the two ends of the flexible cable are connected to external connectors mounted in an air bag inflator or a horn switch.
When a driver turns the steering wheel in either of the two directions while driving a vehicle, the housing mounted on the steering wheel turns in the same direction as that of the steering wheel, winding or unwinding the flexible cable in the rotary connector depending on the direction of turning of the steering wheel. In either state, electrical connection between the rotor and the stator is maintained by the flexible cable of the rotary connector.
When the rotary connector is assembled in the steering device of a vehicle, the flexible cable must be assembled in a state wherein it can be wound or unwound by almost the same amount from a reference position associated with the neutral turning position of the steering wheel.
Hence, the rotary connector is provided with a locking mechanism for maintaining the two housings at the neutral turning position until the rotary connector is assembled in a steering device. Such a rotary connector is designed such that free turning of the two housings is impeded, until the rotary connector is assembled in the steering device, by the locking member mounted relative to the two housings which have been positioned at the neutral turning position. The locking member is removed from the two housings when one of the housings is fixed the steering column.
In recent years, the number of circuit parts provided on the steering wheel of a vehicle have began to increase. That is, there is an increasing demand for providing, on the pad of a steering wheel, control switches for, for example, an automatic cruise control circuit or an air conditioner circuit, in addition to the air bag inflator and the horn switch. An increase in the number of circuits connected by the rotary connector inevitably increases the number of conductors of the flexible cable. However, the space near the steering device is limited, and an increase in the width of the flexible cable is thus restricted. As a result, the electrical insulation distance between the conductors is reduced, and this makes insulation of the conductor used for an air bag more important than the insulation for other conductors because a larger amount of current compared to that which flows in other conductors, flows in the air bag conductor to actuate the air bag inflator.
However, in the case of the aforementioned direct connector, since the terminals are connected directly to the conductors in the connector provided on the housing by, for example, spot welding or soldering, a decrease in the pitch between the conductors, caused by an increase in the number of conductors of the flexible cable, reduces the distance between the adjacent connecting portions, thus reducing the electrical insulation distance. Thus, the direct connector is not suited for connection of multiple circuits.
In view of the aforementioned problems of the prior art, an object of the present invention is to provide a rotary connector which is suitable for use in connection of multiple circuits.
U.S. Pat. No. 5,230,713 discloses the direct coupling type rotary connector in which connectors connected to the two ends of the flexible cable are provided on the housings so as to achieve direct connection with external devices, such as an air bag inflator. In such a rotary connector, since the connectors are formed integrally with the housings, electrical connection between the flexible cable and the external devices is obtained at the same time as the assembly of the rotary connector in the steering device, thus simplifying the connection process between the rotary connector and the external devices.
However, in the direct coupling type direct connector, since a plurality of terminals thereof are exposed from the housing, a provided member must be covered on the direct connector for the purpose of preventing deformation of these terminals and enhancing the dust prevention property. Accordingly, in the assembly process of the rotary connector, the aforementioned locking member and the cover member must be mounted separately, making the assembly operation complicated. Further, in the inspection process conducted after assembly of the rotary connector in the steering device to check whether or not the rotary connector has been accurately connected to the external devices, electrical characteristics are satisfied only if the cover member has been removed and the external devices have been connected to the direct connector. Thus, if the locking member is left unremoved, it is impossible in the inspection process to check whether or not the locking member has been improperly left connected to the rotary connector during assembly.
In view of the aforementioned problems of the prior art, a second object of the present invention is to provide a rotary connector which prevents accidental unremoval of a locking member.